Automated conveyor systems are often used to assemble intricate or delicate work pieces. Pallet-type carriers which ride on top of the conveyors are used to transport the work pieces from one work station to another in the system. A pallet-type carrier usually consists of a flat pallet used to carry a work piece and a lower shoe or puck that rides on top of the moving conveyor. The shoe may also be referred to as a pallet guide.
Pallet-type carriers will often transport a work piece from one station to another in a condition where the work piece is not completely assembled or in a very fragile state. It is imperative to keep the work piece and the pallet, on which the work piece rests, in a horizontal position when transporting the work piece from one station to another station because loose parts that are not securely attached to the work piece may fall off of the pallet between work stations. Further, loose parts may fall off the pallet or become dislodged when the carrier makes a sharp turn, such as a 90.degree. turn. Any tilt of the pallet, in combination with the natural centrifugal forces exerted on the work piece during a sharp turn, can damage the work piece or cause loose parts to be dislodged during the turn.
Therefore, there is a need for stabilized pallet-type carriers for use on automatic conveyor systems. The stabilized pallet-type carriers must be able to transport work pieces from one station to another in a smooth fashion and maintain the general flat or horizontal position of the pallet while the carrier is being transported on the conveyor. Further, the stabilized pallet-type carrier must be able to make sharp turns while maintaining the general flat or horizontal position of the pallet.
Another feature of the pallet-type carrier that can affect the performance of the entire system is the shoe or pallet guide. The shoes often are shaped like a hockey puck and therefore may be commonly referred to as "pucks". The pallet guides or shoes are currently provided in two forms. First, a polyurethane shoe is popular with manufacturers because it is lightweight, requires less energy to transport on top of the conveyor and, because of its lightweight, can reduce the amount of friction between the undersurface of the shoe and the top of the conveyor.
However, polyurethane shoes have not proven entirely satisfactory over time. Specifically, the polyurethane shoes tend to wear prematurely. When used in environments where dust, dirt and grime are present, dirt particles become embedded in the polyurethane shoe. When the polyurethane shoe, embedded with dirt particles, passes over the conveyor, the resulting action is much like rubbing sandpaper on top of the conveyor. As a result, the conveyor chains wear prematurely.
A second type of shoe is one fabricated entirely out of metal. Metal shoes last longer than polyurethane shoes. Further, dust, dirt or grime particles do not become embedded in the undersurface of the metal shoes and therefore the undersurface of the metal shoes remains smooth and does not cause premature wear to the conveyor chain.
However, the metal shoes are much heavier than the polyurethane shoes and when a plurality of pallet-type carriers are employed on a single conveyor, the overall weight transported by the carrier is increased dramatically. Therefore, there is a need for an improved shoe or pallet guide for pallet-type carriers that combines the lightweight of polyurethane or other polymeric materials with the superior wear characteristics of metal shoes, including steel shoes.